Partnering with equipment makers to advance flow
Laurent Pichon describes some recent advances in solid handling and particle engineering at MEPI
Flow chemistry is still evolving after 25 years. Equipment makers are increasingly listening to market expectations. This is a very dynamic trend and is more than encouraging for the future of this technology. MEPI( Maison Européenne des Procédés Innovants), a non-profit industry partnership organisation based at the Institut National Polytechnique de Toulouse in France has been working on some of these.
Flow synthesis
Even if elementary fluorinations1, 2, nitrations3, sodium azide chemistry, lithiations, oxidations and other energetic reactions are still leading the way in flow chemistry, the demand for the downstream processes to be turned into a continuous regime is increasing.
In this respect, MEPI tested pressure differential membrane separators for liquid / liquid( L / L) or liquid / gas( L / G) separations both at laboratory and pilot scales. The expertise here lies in the chemical treatment of the membrane to render it hydrophilic or hydrophobic, and in pore sizes. These devices allow emulsions to be split promptly and swap solvent in cascading flow steps or L / L extractions.
Flow crystallisation
Extensive testing was also done on flow crystallisation using multiple technologies:
• Continuous oscillatory baffled reactor( COBR)
• Mixed suspension mixed product removal( MSMPR)
• Taylor Couette reactor( LCTR)
Unlike static mixers, these dynamic or active reactors offer excellent mixing at low flow rates, with larger channel diameters. They make solid formations possible during chemical reactions, but have so far been more used in crystallisations. Both cooling and anti-solvent crystallisations were tested for organic and inorganic chemistries, with various results upon the type of reactor and configurations.
COBR and MSMPR reactors use pulsation devices for their agitation. Various parameters like flow rates, temperature ramp and the amplitude and frequency of the pulsations can be set up. By contrast, LCTR reactors use rotation and the possible parameters include flow rates, temperature ramp, rotation speed and the gap in between the two cylinders. With proper fine-tuning of these parameters, it is possible to control the size and distribution of the particles, as well as their morphology. This gives access to a‘ two in one’ flow strategy to match a client’ s specifications directly, while batch crystallisation is often followed by batch micronisation to meet the targeted granulometry.
We were able to deliver two different crystal sizes, starting from the same crude solution. This means that several final applications can be served at the same time. For example, in pharmaceuticals, it becomes possible to make larger crystals for caps and smaller one for inhalation products. In addition, flow crystallisations may be five to 20 times faster than the same in batch mode, allowing interesting capex and opex savings.
This new area of particle size engineering via flow crystallisation is attracting the attention of many application markets including pharmaceuticals and energetic materials for defence and aerospace.
Continuous filtration & drying
After flow synthesis and flow crystallisations, a logical next step was to test new technologies for continuous filtration, washing and drying. That was investigated
48 SPECIALITY CHEMICALS MAGAZINE ESTABLISHED 1981